Fuel cell module

ABSTRACT

A fuel cell module includes a number of series-connected fuel cells which collectively form a fuel cell stack in such a way that the magnetic field or stray field that is generated during the operation of the fuel cell module and that is detectable in an outer area is kept particularly small. To this end, the invention provides that a number of shielding lines that are connected to a first pole flange of the fuel cell stack are provided, these shielding lines being guided on the outer area of the fuel cell stack, as far as a contact area to a second pole flange of the fuel cell stack.

[0001] The invention relates to a fuel cell module having a number ofseries-connected fuel cells which are combined to form a fuel cellstack.

[0002] Fuel cells may be used for environmentally friendly generation ofelectricity. A process which essentially represents the converse ofelectrolysis takes place in a fuel cell. A fuel which includes hydrogenis supplied to an anode in a fuel cell, and an auxiliary substance whichincludes oxygen is supplied to a cathode. The anode and cathode are inthis case electrically isolated from one another via an electrolytelayer, in which case, although the electrolyte layer allows ions to beexchanged between the fuel and the oxygen, the electrolyte layerotherwise ensures that the fuel and the auxiliary substance areseparated in a gastight manner. As a consequence of the exchange ofions, hydrogen which is included in the fuel can react with the oxygento form water, with electrons being enriched on the fuel-side electrodeor anode, and electrons being absorbed on the auxiliary substance sideelectrode or cathode. During operation of the fuel cell, a usablepotential difference or voltage is thus formed between the anode andcathode, with the only waste product from the electricity generationprocess being water. The electrolyte layer which, in the case of ahigh-temperature fuel cell, may be in the form of a ceramic solidelectrolyte, or in the case of a low-temperature fuel cell may be in theform of a polymer membrane, thus has the function of separating thereactants from one another, of carrying the charge in the form of ions,and of preventing an electron short circuit.

[0003] Owing to the electrochemical potentials of the substances thatare normally used in a fuel cell such as this, an electrode voltage ofabout

[0004] 0.6 to 1.0 V can be formed in normal operating conditions, andcan be maintained during operation. For technical applications in whicha considerably higher total voltage may be required depending on thepurpose or the planned load, a number of fuel cells are thus normallyconnected electrically in series in the manner of a fuel cell stack,such that the sum of the electrode voltages produced by each of the fuelcells corresponds to or is greater than the required total voltage.Depending on the required total voltage, the number of fuel cells in afuel cell stack such as this may, for example, be 50 or more.

[0005] In order to make use of the potential difference which isgenerated during operation of the fuel cells that are joined together soas to form such a fuel cell stack, the circuitry of the fuel cell stackis provided with a load. In this case, a so-called pole plate, to whichthe electrical input and output cables can be connected, is arranged oneach of the two outermost series-connected fuel cells in the fuel cellstack, in order to provide the electrical connection for the load.

[0006] Owing to the particular operating characteristics of such fuelcells and, in particular, with respect to the generation of just wateras the only significant waste product, fuel cells are also particularlysuitable for use for power supplies in intrinsically closed mobilesystems, such as underwater vehicles. In this case, it is particularlyadvantageous that a comparatively high output current at a normalvoltage level can be achieved with only restricted physical dimensions,in the form of comparatively high power density in a fuel cellarrangement. Furthermore, particularly when used in underwater vehicles,the fuel, that is to say the substance which includes the hydrogen, canbe produced in a comparatively compact form. In this case, pure oxygenmay be used

[0007] as the auxiliary substance or oxidant. In this case, the hydrogenmay in particular be stored in hydride tanks.

[0008] When fuel cells are actually used in an underwater vehicle, itmay be desirable to keep the signature that is emitted to the exterior,that is to say the externally detectable indications of operation of theunderwater vehicle, particularly low. This signature may also includemagnetic fields, which are produced by the currents that flow in and outduring operation of fuel cells.

[0009] The invention is thus based on the object of specifying a fuelcell module having a number of series-connected fuel cells which arecombined to form a fuel cell stack, in which the magnetic field or strayfield which is produced during its operation and can be detected in anexternal area is kept particularly low.

[0010] According to the invention, this object is achieved in that anumber of shielding cables are provided, which are connected to a firstpole plate of the fuel cell stack and are routed on the external area ofthe fuel cell stack along its stacking direction as far as a contactarea for a second pole plate of the fuel cell stack.

[0011] The invention is in this case based on the idea that the magneticfield which can be detected in the external area of the fuel cell moduleduring its operation can be kept particularly low by magneticallycompensating for the operating currents to a particularly large extentin some suitable manner. Magnetic computation may in this case becarried out by that spatial area in which a significant operatingcurrent occurs being surrounded in a suitable manner by current returnpaths, in the manner of a coaxial arrangement. The current return pathsshould in this case be designed such that a compensation current whichflows there in the opposite direction to the operating currentcompensates sufficiently for the magnetic field produced in the externalarea by

[0012] the operating current. In the case of a fuel cell stack whichcomprises a number of series-connected fuel cells, a significant currentoccurs in the fuel cells themselves during operation, owing to theactivity of the fuel cells. This operating current should bemagnetically shielded to an adequate extent by suitable routing ofcurrents in the opposite direction. For this purpose, the shieldingcables are routed along the external area of the fuel cell stack.

[0013] Advantageous refinements of the invention are the subject matterof the dependent claims.

[0014] A particularly uniform shielding effect in the external area ofthe fuel cell module can be achieved in that, in one advantageousrefinement, the shielding cables are arranged symmetrically around thecentral axis, which is extended in the stacking direction, of the fuelcell stack. A refinement such as this is particularly reliable forshielding the magnetic field when the fuel cell stack has anapproximately square cross section with respect to its central axis.

[0015] In an alternative or additional advantageous refinement, theshielding cables are arranged at approximately uniform intervals on thecircumference of the cross section, determined in the stackingdirection, of the fuel cell stack. A refinement such as this is alsoparticularly suitable for reliable shielding of the magnetic field whenthe fuel cell stack does not have a square cross section, for examplehaving a rectangular cross section. In this case, for example, if thefuel cell stack were to have a cross section with a length-to-widthratio of approximately 2 to 1, it would be possible to provide for twoshielding cables to be arranged on each of its longitudinal faces andone shielding cable to be arranged on each of its width faces, with eachshielding cable being at an a approximately uniform distance from therespective shielding cables adjacent to it in this case.

[0016] In order to allow the shielding cables to be connected in aparticularly simple manner to a power cable which continues further, theshielding cables are advantageously joined together in the contact areato form a first connecting contact, also referred to as a star point orcurrent node. The contact can then be produced to a connecting point ordirectly to a load from this connecting contact via, for example, asingle conductor which continues further. The current which is carriedby the shielding cables is combined by the connecting contact at onepoint, from where it is passed on further. If the contact to aconnecting point or to the load is produced, for example, by a number ofcables, then the connecting contact—even if the currents are notdistributed uniformly between the shielding cables—results in a uniformdistribution of the currents in the cables which continue further. Thismeans that the stray field from the fuel cell module is independent ofexternal influences.

[0017] In order to keep the stray magnetic field particularly low inthis refinement, an additional advantageous development provides for anumber, corresponding to the number of shielding cables, of connectingcables to be arranged on the second pole plate of the fuel cell stack,which are joined together to form a second connecting contact, with eachconnecting cable being routed in the contact area in the immediatevicinity of a respective shielding cable. This arrangement results in aparticularly simple manner in each current-carrying cable beingimmediately adjacent to a further cable, which carries approximately thesame current level in the opposite direction. The area which issurrounded by the current and the return current and which canessentially be used as a measure of the stray magnetic field thatresults in the external area is kept particularly small with thisarrangement.

[0018] In order to electrically connect a load to fuel cell moduleswhich are designed in this way and have low stray fields in somesuitable manner with low stray fields as well, a further advantageous

[0019] refinement provides for the first pole plate to be connected to apower cable, and for the second pole plate to be connected to a powercable system which surrounds the power cable in the manner of a coaxialarrangement. These connections may in this case be produced inparticular with the interposition of said first or second connectingcontent.

[0020] The advantages which are achieved by the invention are, inparticular, that any stray magnetic field which can be detected in theexternal area of the fuel cell module is kept particularly low byreturning the operating current, which flows through the fuel cell stackduring this operation, along the external area of the fuel cell stack asfar as the contact area for the corresponding pole plate. This isbecause, in this arrangement, the operating current which flows in thefuel cell stack is surrounded in the external area of the fuel cellstack by return currents which flow in the opposite direction and whoseoverall magnitude corresponds to the operating current. Reliableshielding of the operating current which flows in the fuel cellsthemselves is thus also ensured for the actual fuel cell module, in theform of a coaxial arrangement.

[0021] An exemplary embodiment of the arrangement will be explained inmore detail with reference to a drawing, in which the FIGURE shows afuel cell module.

[0022] The fuel cell module 1 shown in the FIGURE has a number of fuelcells 2. The fuel cells 2 are electrically connected in series and arespatially combined to form a fuel cell stack 4. Each fuel cell 2 in thiscase has two flat electrodes, which are physically and electricallyisolated from one another via an electrolyte. The electrodes of eachfuel cell 2 are each directly connected to the electrodes facing them onthe fuel cells 2 that are adjacent to them. The first and last fuelcells 2 seen in the stacking direction of the fuel cell stack 4

[0023] as indicated by the arrow 6 are, in contrast, connected by theirelectrode, which is arranged on the respective edge of the fuel cellstack 4, to a negative pole plate or first pole plate 8 and,respectively, to a positive pole plate or second pole plate 10.

[0024] The first pole plate 8 and the second pole plate 10 are in thiscase used for the outward and return supply of an operating current forthe fuel cell stack 4 during its operation. This is because therecombination of the hydrogen and of the oxygen in the materials thatare supplied to the fuel cells 2 during operation of the fuel cell stack4 results in a redistribution of electrons, which on the one hand leadsto the usable potential difference described above, and on the otherhand corresponds in the steady state to an operating current through thefuel cell stack 4. This operating current produces a stray magneticfield in the external area of the fuel cell stack 4. However, the fuelcell module 1 is designed such that this stray magnetic field is keptparticularly low.

[0025] For this purpose, the first pole plate 8 of the fuel cell stack 4is connected to a number of shielding cables 12. The shielding cables 12are arranged on the external area of the fuel cell stack 4, along itsstacking direction as indicated by the arrow 6, and are intended toprovide the return path for the operating current, which flows throughthe fuel cells 2 in the interior of the fuel cell stack 4, into the areaof the second pole plate 10. This essentially results in a coaxialarrangement of a first conductor, which is essentially provided by thefuel cell stack 4, with a number of second conductors which surround it.Since the current flows in the opposite direction in the first conductorand in the second conductors, the magnetic field which is produced bythe currents in the external area of the fuel cell stack 4 isapproximately compensated for, in particular because the current whichis carried in the first conductor or fuel cell stack 4 and the returncurrent which is carried overall in the second conductors or

[0026] shielding cables 12 are of the same magnitude. The shielding ofthe stray magnetic field in the external area of the fuel cell stack 4is in this case particularly comprehensive in the spatial area a longdistance away; in the near area directly around the fuel cell stack 4,on the other hand, stray fields may still occur owing to geometryaffects—in particular since the current is not returned in an envelopethat completely surrounds the fuel cell stack 4.

[0027] The shielding cables 12 are routed on the external area of thefuel cell stack 4 as far as a contact area 14 for the second pole plate10 of the fuel cell stack 4. The shielding cables 12 are joined togetherin the contact area 14 to form a first connecting contact 16, which isconnected to a power cable 18. The power cable 18 is itself connected,in a manner which is not illustrated in any more detail, to a load whichis to be fed from the fuel cell module 1.

[0028] Furthermore, the fuel cell module 1 is also designed to keep thestray magnetic field which may be produced by the shielding cables 12 inthe contact area 14 as low as possible. For this purpose, a number,which corresponds to the number of shielding cables 12, of connectingcables 20 originate from the second pole plate 10 and are joinedtogether in order to form a second connecting contact 22. The connectingcables are in this case physically routed such that one connecting cable20 in each case comes to rest in the immediate vicinity of a respectiveshielding cable 12 in the contact area 14. This arrangement results inthe stray magnetic field which is produced by the current flowing in ineach case one shielding cable 12 being approximately compensated for orcancelled out by the current flowing in the opposite direction in theconnecting cable 20 which is in each case associated with this shieldingcable 12. In other words, the overall stray magnetic field which isproduced by a pair of cables which are in each case defined by ashielding cable 12 and an associated connecting cable 20 is keptparticularly low, especially since the area

[0029] which is surrounded by the cable pair, that is to say therespective shielding cable 12 and the respective connecting cable 20, iskept particularly small.

[0030] The second pole plate 10 is connected via the connecting cables20 and via the second connecting contact 22 formed by them to a powercable system 24, which surrounds the power cable 18 in the manner of acoaxial arrangement. In the exemplary embodiment shown in the FIGURE,the power cable system 24 is in this case provided by a first conductor26 and by a second conductor 28, which surround the power cable 18 atthe sides. However, alternatively, a greater number of conductors or asheath, for example a cylindrical sheath, which completely surrounds thepower cable, may also be provided in order to form the power cablesystem 24.

[0031] The fuel cell stack 4 and, together with it, the fuel cells 2which form it have an approximately square cross section in theexemplary embodiment. In order to achieve a particularly good shieldingeffect matched to this, the shielding cables 12 are arrangedsymmetrically around a central axis, which is extended in the stackingdirection as indicated by the arrow 6, of the fuel cell stack 4. In thiscase, one shielding cable 12 is in each case arranged centrally, inparticular on each outer face of the square cross section. This alsoresults in the shielding cables 2 being spaced apart approximatelyuniformly on the circumference of the cross section, determined in thestacking direction, of the fuel cell stack 4. However if the fuel cellstack 4 has a cross-sectional shape other than the square shape, theshielding cables 12 may also be routed in some other way, matched to therespective cross-sectional shape. For example, if the fuel cell stack 4were to have a rectangular cross section, it would be possible todistribute a number of shielding cables 12 on the circumference of thecross section such that the ratio of the number of shielding cables 12routed on the longitudinal face of the rectangular cross section to thenumber of

[0032] shielding cables 12 routed on the narrow face of the rectangularcross section is approximately equal to the ratio of the length of thelongitudinal face to that of the narrow face.

1. A fuel cell module (1) having a number of series-connected fuel cells(2) which are combined to form a fuel cell stack (4) and in which anumber of shielding cables (12), which are connected to a first poleplate (8) of the fuel cell stack (4), are passed to the external area ofthe fuel cell stack (4) along its stacking direction as far as a contactarea for a second pole plate (10) of the fuel cell stack (4).
 2. Thefuel cell module (1) as claimed in claim 1, in which the shieldingcables (12) are arranged symmetrically around a central axis, which isextended in the stacking direction, of the fuel cell stack (4).
 3. Thefuel cell module (1) as claimed in claim 1, in which the shieldingcables (12) are arranged at approximately uniform intervals on thecircumference of the cross section, determined in the stackingdirection, of the fuel cell module (1).
 4. The fuel cell module (1) asclaimed in one of claims 1 to 3, whose shielding cables (12) are joinedtogether in the contact area (14) to form a first connecting contact(16).
 5. The fuel cell module (1) as claimed in claim 4, from whosesecond pole plate (10) a number, which corresponds to the number ofshielding cables (12), of connecting cables (20) originate and arejoined together to form a second connecting contact (22), with eachconnecting cable (20) being routed in the contact area (14) in theimmediate vicinity of a respective shielding cable (12).
 6. The fuelcell module (1) as claimed in one of claims 1 to 5, in which the firstpole plate (8) is connected to a power cable (18) and the second poleplate (10) is connected to a power cable system (24) which surrounds thepower cable (18) in the manner of a coaxial arrangement.
 7. The fuelcell module (1) as claimed in one of claims 1 to 5, in which the firstpole plate (8) and the second pole plate (10) are connected to at leasttwo respective power cables (18), with the power cables (18) of thefirst pole plate (8) being arranged symmetrically with respect to thepower cables (18) of the second pole plate (10).